# N: Interactions in nuclear systems

### Research areas

• Experimental nuclear physics
• Theoretical nuclear physics

### Goals

Project N is dedicated to the experimental and theoretical study of nuclei as strongly interacting systems using electro-weak probes. We aim at developing a systematic understanding by combining state-of-the-art theoretical methods with cutting edge experiments.

The main highlights of project N will be:

1. Few-body interactions
To shed light on the recent tension found between modern theory and new precise experimental data on the monopole transition form factor of $$^4$$He, we will perform an order-by-order analysis of the chiral expansion using local interactions. We will also use the new MAMI data to constrain three-nucleon forces.
2. Light muonic atoms
To support the CREMA experimental campaign, we will continue our very successful theoretical program for the ab-initio calculation of nuclear-structure corrections in muonic atoms. We will finalize our study of the hyperfine splitting in muonic deuterium and perform new calculations for the Lamb shift in muonic $$^{6,7}$$Li$$^{2+}$$.
3. Electro-weak response functions
The successful coupled-cluster theory will be used to compute, for the first time, general electro-weak response functions at finite momentum transfer with the full final state interaction. Chiral effective field theory will be used to assess theoretical uncertainties. An inclusive electron-scattering experiment on $$^{16}$$O will be performed at MAMI to benchmark this new theory.
4. Transverse asymmetry measurements on $$^{208}$$Pb
The successful experimental program will be extended to $$^{28}$$Si, $$^{40}$$Ca and $$^{208}$$Pb. An improved experimental set-up will allow the first measurement at MAMI of the surface thicknesses of $$^{208}$$Pb in parity-violating electron scattering.
5. Systematic study of coherent $$\pi^{0}$$ photoproduction reactions on medium-mass nuclei
The newly developed theory will be complemented with a model of the $$\pi^0$$-nucleus interaction in the final state. The theoretical prediction will be compared to the measured Sn-isotopic chain, the previously published $$^{208}$$Pb data and the data on $$^{40,48}$$Ca taken during the second funding period.
6. Detector simulations and detector development for nuclear astrophysics program at MESA
Given the time schedule for the commissioning of the MESA accelerator and the P2 experiment, in the third funding period we will perform systematic studies to optimize the detector configuration, as well as extensive beam tests for the Mainz Radius Experiment (MREX). A new tagging-detector for future programs in nuclear structure and astrophysics will be developed and commissioned at the A1 spectrometer facility.